1. Field of the Invention
The present invention relates to electromechanically actuated valves, such as intake and exhaust valves of an internal combustion engine, and to electromechanical actuators therefore.
2. Description of Related Art
Electromechanically actuated valves have been developed for use as intake and exhaust valves for internal combustion engines. Such electromechanically actuated intake and exhaust valves are mounted on the engine cylinder head to provide variable valve timing that offers the opportunity to better control and operate the internal combustion engine.
A so-called constant or single lift electromechanical valve actuator includes first (upper) and second (lower) electromagnets between which an armature disk on a valve-actuating shaft resides for movement between the electromagnets. The actuator is mounted on the cylinder head above the conventional intake or exhaust valve, valve closing spring, and valve retainer in such a manner that the valve-actuating shaft of the actuator engages an end of the valve stem to actuate the valve. The upper electromagnet is energized to close the valve and the lower electromagnet is energized to open the valve with valve lift being equal to the distance between the bottom of the armature disk and the top of the lower electromagnet where valve travel stops. Movement of the valve has been guided by first and second valve stem guides that are fixed in position in the respective first and second electromagnets and a conventional valve guide fixed in position in the cylinder head. Engines equipped with constant lift electromechanically actuated intake and exhaust valves typically have a constant lift optimized for maximum torque and power. However, such engines suffer from poor combustion stability at light engine loads as a result of very low in-cylinder air-fuel mixture turbulence at such loads and also suffer from poor noise-vibration-harshness (NVH) due to high air dynamics noise.
Attempts have been made to develop so-called dual lift electromechanically actuated intake and exhaust valves that provide variable valve timing and variable lift to provide higher in-cylinder air-fuel mixture turbulence at light engine load and high gas flow at high engine load. One type of dual lift electromechanically actuated valve includes the aforementioned first and second electromagnets and the armature disk therebetween to move and hold the valve at a first lift position (full open valve position) relative to the valve closed position and an additional third electromagnet and second armature disk connected to the valve stem in a manner to move and hold the valve at a second lift position (mid-open valve position) relative to the closed valve position. Each electromagnet must remain energized to hold the valve at the respective closed, full open, and mid-open valve position during engine operation. U.S. Pat. Nos. 5,647,311; 5,692,463; and 5,765,513 describe such dual lift electromechanically actuated valves.
The present invention provides a dual coil, dual lift electromechanical valve actuator that provides a closed valve position, first high lift position, and second low lift position wherein the second low lift position of the valve is maintained without the need for supply of electrical current to the actuator.
In an illustrative embodiment of the invention, the actuator comprises a movable valve-actuating shaft for actuating the valve. The valve-actuating shaft may be engaged end-to-end with a valve stem of the valve or may be integral with the valve stem. The actuator includes a first valve-closing electromagnet and a second valve-opening electromagnet spaced apart along a length of the valve-actuating shaft with an armature of the valve-actuating shaft disposed between the first and second electromagnets. To change from high to low valve lift operation, the armature is moved by energization of the first electromagnet to a first armature position that establishes the valve closed position and by energization of the second electromagnet to a second armature position that establishes the first high lift position of the valve relative to a valve seat. The actuator further includes a tubular guide member which receives the valve-actuating shaft and which is movable relative thereto to a location between the first and second electromagnets to define a third armature position where the armature resides on the guide member when the first and second electromagnets are de-energized to establish the second low lift position relative to the valve seat. The guide member is retained at the location with a mechanical latch, while a valve closing spring force and valve opening spring force are provided to hold the valve at the second low lift position while the first and second valve closing electromagnets are de-energized. The valve thereby is maintained at the second low lift position without the need for electrical current to be supplied to the actuator.